This invention relates to a control apparatus for an electric motor car, more particularly a battery car having a battery and a fuel engine driven generator for float charging the battery, usually called a hybrid car.
Recently, the problem of contaminating the atmosphere by gas exhausted from the internal combustion engines of motor cars has become important from the standpoint of public health, and various regulations for the content of exhaust gas are being enforced. Accordingly, research is being conducted in many countries regarding harmless electric motor cars or hybrid cars.
However, in a hybrid car having a horse power comparable with that of an ordinary gasoline engine driven motor car, about one-third of the weight of the car is due to electric components, including a battery, an electric motor and a controller. With a battery car, the running distance for each charge is only about 100 kilometers. Where it is necessary to frequently stop and run the car, as occurs when traveling through a city area, the running distance per charge decreases further. Even when a more efficient battery is developed in the future, due to the losses occurring at the time of charging and discharging, it will be necessary to charge the battery with an energy higher than that of the discharge.
Accordingly, for the purpose of increasing the running distance of a hybrid car and obtaining high speed characteristics comparable with those of conventional gasoline engine driven motor cars it has been proposed to use an engine driven generator for float charging the battery. With this type of an electric motor car, so long as a variable load is imposed upon the engine as in conventional motor cars, the amount of exhaust gas can not be decreased because the exhaust gas is relatively clear or harmless and the fuel efficiency is high only when the internal combustion engine is operated at a constant speed and under a constant load. It is known that when an ordinary motor cars runs through a city area the fuel efficiency drops to about one-third of the best value because it is necessary to frequently stop and run the car or to operate the engine under load and no load conditions.
It is a recent trend to use a hybrid car wherein a brushless three phase alternator is used, the AC output power of the alternator is rectified to obtain direct current for charging a battery, and a variable frequency, variable voltage inverter is used to convert the battery power into three phase alternating current which is used to energize a three phase induction motor that drives the car. This system has the same problems as those described above.